Adsorptive removal of Bisphenol A by biomass activated carbon and insights into the adsorption mechanism through density functional theory calculations

Activated carbon was synthesized from Tithonia diversifolia biomass using potassium hydroxide as the chemical activating reagent. Taguchi's experimental design approach was applied to determine the best preparation conditions. An optimum 2:1 impregnation ratio and 700 °C activation temperature produced the best carbon with a high 854.44 m²g^-1 surface area, 0.445 cm³g^-1 total pore volume and 18.3% yield. From the analysis of variance (ANOVA), the impregnation ratio was found to be the most influential factor in preparing activated carbon with the maximum surface area. SEM and XRD studies revealed the porous microcrystallite structure of the obtained activated carbon. Batch adsorption studies were performed to test the efficiency of Tithonia diversifolia activated carbon for the removal of Bisphenol A (BPA) from aqueous solution. A maximum 98.2% removal percentage was attained at optimum conditions of 0.2 g adsorbent dose, pH 7, 80 min contact time and 40 mg L^?1 initial BPA concentration. The Langmuir isotherm model described the equilibrium adsorption of BPA well with a maximum adsorption capacity(q_m) of 15.69 mg g^?1 while the kinetic adsorption study indicated a pseudo second order model. A theoretical investigation suggested that the adsorption of BPA onto the activated carbon mainly proceeds via chemisorption and the presence of a carboxyl functional group on the activated carbon surface yielded a greater adsorptive impact on BPA. This study indicates that Tithonia diversifolia could be used as a potential raw material for preparing activated carbon for removing of BPA from water.     

Accuracy of high-resolution rectal magnetic resonance imaging re-staging with histopathology in locally advanced rectal cancer after neoadjuvant chemoradiotherapy

Background/objectiveRe-staging of locally advanced rectal cancer (LARC) following neoadjuvant chemoradiotherapy (NCRT) is a crucial step in surgical decision-making. Currently, MRI is the imaging of choice for evaluation of LARCs, however, the diagnostic accuracy of this modality is inconsistent. In this study, we evaluated the diagnostic accuracy of MRI in LARC and analyzed the factors that influenced the accuracy.MethodsThe records of 133 patients diagnosed with LARC who were operated on during 2011–2018 were retrospectively reviewed. All patients received NCRT followed by re-staging based on high-resolution rectal MRI. The MRI results were analyzed for their yT and yN accuracy and anal sphincter involvement and compared with the related histopathological studies after definitive surgery.ResultsRe-staging MRIs gave overall accuracy in both the yT stage and yN evaluation of 85% (K 0.45 and 0.21, respectively). The MRI tended to overstaging for tumor invasion and understaging for lymph node involvement (sign test p-values = 0.017 and 0.022, respectively.) The highest accuracy of the yT stage was yT4b (93%, K 0.71). The study found that larger tumors (>3 cm) were associated with significantly higher accuracy in the yT readings while lack of lymphovascular invasion was associated with higher accuracy in the yN readings. The negative predictive value for anal sphincter involvement was 100%.ConclusionMRI has limited accuracy in post-NCRT re-staging in LARC, tending to give overstaged yT readings and understaged yN readings. An MRI exclusion of sphincteric involvement is highly reliable.